According to the UN’s Intergovernmental Panel on Climate Change (IPCC), CO2 concentrations of “about 450ppm or lower are likely to maintain warming below 2 degrees Celsius over the 21st century relative to pre-industrial levels.” But lead author on the paper Richard Betts said we could pass that number in 20 years or less. He told the Guardian that even if we reduce emissions immediately, we might be able to delay reaching 450ppm but “it is still looking like a challenge to stay below 450ppm.”

Paper co-author Ralph Keeling said, “Back in September last year, we suspected that we were measuring CO2 concentrations below 400ppm for the last time. Now it is looking like this was indeed the case.”

El Niño has played a role in climbing carbon dioxide levels, but we’ll likely see higher CO2 levels than the last large El Niño storm during 1997 and 1998 because “manmade emissions” have risen by 25 percent since that storm, according to The Guardian.

Met Office experts are fairly confident in these projections. They predicted in November 2015 that in May 2016 “mean concentrations of atmospheric CO2” would hit 407.57ppm. The actual figure was 407.7ppm.

During 2015, NOAA reported that the “annual growth rate” of C02 in the atmosphere rose by 3.05ppm. NOAA lead scientist Pieter Tans said “Carbon dioxide levels are increasing faster than they have in hundreds of thousands of years. It’s explosive compared to natural processes.”